(1) Field of the Invention
The present invention relates generally to signal processing, and more particularly to a new method and apparatus for processing signals received from an array of acoustic pressure-vector sensors using a non-linear processing method.
(2) Description of the Prior Art
An acoustic wave is distinguished by both scalar (pressure) and vector (velocity) fields. Detection of acoustic waves by sensors was initially limited to pressure sensors capable of detecting only the scalar field of acoustic waves. For underwater acoustic detection applications, such as sonar, hydrophones are the pressure sensor of choice, and are often used in arrays of multiple hydrophones.
The majority of acoustic sensor arrays for use in underwater acoustic wave detection employ acoustic pressure sensors, such as hydrophones, and are designed for additive processing of the pressure sensor signals. Some acoustic sensor arrays employing acoustic pressure sensors have been designed for non-linear processing of the pressure sensor signals. The benefit of this type of processing, however, is limited when using only pressure sensors because no acoustic wave vector field information is involved in the array signal processing. A significant drawback to the conventional additive pressure sensor type of acoustic sensor array is the inability to achieve a narrow acoustic beam width without having a large acoustic aperture, particularly where the beam width becomes wider as the acoustic frequency goes lower.
There has been a progression in acoustic wave detection technology with the advent of acoustic vector sensors. Tri-axial acoustic vector sensors measure all three Cartesian components of the vector field of acoustic waves. With the development of acoustic vector sensor technology, it is now possible to combine an acoustic vector sensor with a pressure sensor to form a pressure-vector sensor in order to measure and process the information carried by both the scalar and vector field of an acoustic wave simultaneously.
A single pressure-vector sensor element has an omni-directional directivity for the pressure sensor and a dipole directivity in each axis of a three dimensional space for the vector sensor. A single pressure-vector sensor element provides limited advantages over a single pressure sensor element. However, an array of multiple pressure-vector sensors, properly arranged, can exhibit superior performance over an array of multiple pressure sensors with regard to the reduction of unwanted noise and noise source location. In particular, the use of pressure-vector sensors can significantly reduce the acoustic aperture size of the array if the signals from the pressure-vector sensors are processed correctly.
What is needed is a method for processing signals from an acoustic pressure-vector sensor array that is independent of acoustic frequency and does so for an array having a relatively small acoustic aperture.